Transmission
Genital HPV infection is primarily transmitted by genital
contact, usually through sexual intercourse (20;83).
In virtually all studies of HPV prevalence and incidence,
the most consistent predictors of infection have been
various measures of sexual activity, most importantly,
the number of sex partners (28;31;64;84). Among women,
the risk of acquiring a genital HPV infection increases
with increasing number of lifetime male sex partners
(25;26;84-87). Similar to infection with other STD,
having sex with a new partner may be a stronger risk
factor than having sex with a steady partner (21;31).
With each new partner, an adolescent female substantially
increases her risk of acquiring genital HPV (31). The
source of transmission is usually from persons who
are asymptomatic and do not realize they are infected
(64). Among women who report no previous sexual intercourse,
0–8% have HPV infection supporting the premise
that the major route of transmission is sexual (18-21).

Although less well-examined, another
variable that increases a woman’s risk of HPV
infection is the sexual activity of her partner. A
study of adolescent females found that those with a
partner who had multiple sex partners were at increased
risk of HPV infection (31). A study of college students
in Seattle found that those with male sex partners
with at least one prior partner had a five-fold increased
risk of infection compared to those whose male partners
had no prior partners. Women whose male partners had
an unknown number of prior sex partners had an even
higher (eight-fold) risk for acquiring HPV infection
(21). This study also reported that women who had known
a sex partner at least eight months before initiating
a sexual relationship were less likely to acquire genital
HPV infection. It was hypothesized that this was due
to a greater chance of spontaneous clearance of infection
in men who might have been infected with HPV in a previous
sexual relationship (21).

Other types of genital contact in the
absence of penetrative intercourse (oral-genital, manual-genital,
and genital-genital contact) leading to HPV transmission
have been described, but these routes of transmission
are less common than sexual intercourse (21;88-90).
For example, a recent study of college-aged women in
Seattle reported a two-year genital HPV incidence rate
of 39% among sexually active women and 8% among women
who had not engaged in penetrative vaginal intercourse.
Almost all of the infections in women who had not engaged
in sexual intercourse appeared to be related to genital
contact other than penetrative intercourse (21). This
study also found minimal evidence of HPV transmission
through oral sex (either transmitted from the genital
area to the mouth or the mouth to the genital area)
(21). Genital HPV infection also may be transmitted
by non-sexual routes, but this is extremely uncommon.
Non-sexual routes of genital HPV transmission include
transmission from a mother to a newborn baby, which
is rare (91;92), and transmission by inanimate objects
such as environmental surfaces and clothing, which
has been hypothesized but has never been documented
(93-96).

Prevention of Genital HPV Infection
Prevention
of genital HPV infection is important to reduce the
prevalence of genital warts and abnormal Pap tests,
as well as cervical cancer. Cervical cancer screening
programs have been highly effective in reducing rates
of cervical cancer in the United States (97;98); decreasing
the incidence of genital HPV infection should also
reduce rates of cervical cancer(16).

In general, for a given sexually transmitted
disease, the number of new infections transmitted to
a susceptible population is a function of three variables:
duration of infectiousness, efficiency (likelihood)
of transmission of infection, and number of new sex
partners a person has while infected (99). In the absence
of measures to reduce susceptibility in the population
(such as the use of effective vaccines), strategies
addressing each of these variables can reduce transmission
of infection. Such strategies include reducing the
duration of infectiousness by treatment, decreasing
the efficiency of transmission by measures aimed at
reducing infectivity (e.g., condoms, microbicides),
and reducing the number of sex partners. The following
is a summary of what is currently known about the value
of each of these approaches for preventing genital
HPV infection.

Reducing Duration of Infectiousness
The
most common approach to reducing infectiousness of
an STD is treatment. In contrast to bacterial STD for
which transmission can be prevented through curative
treatment, there is only limited evidence that treatment
of HPV-associated lesions is useful to prevent HPV
transmission. There is no effective systemic therapy
for genital HPV, as exists for bacterial and some other
viral STD. Treatments are directed to lesions associated
with HPV, and HPV infections in the absence of detectable
disease are not treated. Current treatment options
for both genital warts and cervical cancer precursors
include various local approaches that remove the lesion
(e.g., cryotherapy, electrocautery, laser therapy,
surgical excision). Genital warts are also treated
with topical pharmacologic agents (100). Treatment
of genital warts and cervical cancer precursors might
reduce infectiousness (100). Although this premise
is difficult to test directly because assays for infectivity
do not exist, it is supported by several observations.
First, in some studies larger amounts of HPV DNA have
been found in high-grade than in low-grade cervical
lesions (101). Second, after clearance of genital warts
after treatment with immune stimulating drugs (e.g.
imiquimod), the amount of HPV DNA in the skin can be
reduced (102). Third, clearance of HPV DNA can occur
after standard therapy for cervical high-grade lesions
(103-111). However, clinically normal skin and mucosa
near HPV-associated lesions often contain HPV (112;113).
This reservoir is thought to explain the typical recurrence
rates of 10–20% after treatment of cervical lesions
(114;115) and 20–50% after treatment of genital
warts (100). It might also help explain the fact that
treatment of partners does not influence recurrence
rates of genital warts (116). Thus, based on the limited
existing data, currently available therapies for HPV-related
lesions may reduce but probably do not eliminate infectiousness;
the impact of the reduction in viral concentration
which occurs with treatment remains unclear.

Reducing Efficiency of Transmission
Efficiency
of transmission, or the likelihood that an infection
will be transmitted from an infected person to an uninfected
person, can be affected by several variables, such
as immunity. However, for STD, the most common approach
is the use of physical barriers such as condoms. In
the future, other methods that may decrease the likelihood
that an infection will be transmitted could include
chemical barriers, such as microbicides or a combination
of chemical and physical approaches.

Condoms
Evidence for the effectiveness
of the male latex condom to prevent various STD among
heterosexual men and women was the subject of a recent
NIH report (117). The report concluded that for the
majority of STD, published data were not adequate to
definitively assess the effectiveness of condoms to
prevent STD. The review also concluded that most epidemiologic
studies that evaluated condom use had significant methodologic
problems. For HPV specifically, the NIH report concluded
that most of the reviewed studies did not obtain sufficient
information on condom use to allow careful evaluation
of the association between condom use and HPV infection
or disease. The report also concluded that there was
no epidemiologic evidence that condom use reduced the
risk of HPV infection, but that condom use might afford
some protection in reducing the risk of HPV-associated
diseases, including warts in men and cervical neoplasia
(cervical cancer precursors and invasive cancer) in
women (117). More recently, an even more detailed review
of the published literature on condoms and HPV infection
and its sequelae came to similar conclusions as the
NIH report and elaborated on the many methodologic
issues affecting studies of condoms for HPV prevention
(118). In addition, several other recent studies reported
that, for women and men, use of male condoms reduces
the risk of genital herpes and chlamydia, both of which
may be co-factors for the development of cervical cancer
(81;82;119-124). Below is a summary of current scientific
evidence on the effectiveness of male condoms for prevention
of genital HPV.

As described above, available clinical
and epidemiologic data indicate that genital HPV infection
is transmitted by contact with infected skin or mucosa.
Laboratory studies have demonstrated that latex condoms
provide an essentially impermeable barrier to particles
the size of HPV (125;126). Studies of HPV infection
in men demonstrate that most HPV infections (both HPV
DNA and HPV-associated lesions) are located on parts
of the penis that would be covered by a condom (48;54-57;63;127-129).
However, even consistent and correct use of condoms
would not be expected to offer complete protection
from HPV infection because infections also may occur
on sites not covered or protected by a condom. In men,
HPV infection can occur on the scrotum, groin area,
base of the penis, and anus (54-57). In women, HPV
infection can occur on the outside of the vulva, which
can come into contact with the genital skin of a man
using a condom.

Published studies that have assessed
the effectiveness of male condoms to prevent HPV infection
or any STD other than HIV are limited by multiple methodologic
issues (117;118). In general, these limitations are
likely to underestimate condom effectiveness (130-132).
Studies with optimal designs would collect information
on consistent and correct condom use and would be able
to determine whether HPV infection preceded or followed
condom use. In addition, several recent studies have
demonstrated that many individuals use condoms in situations
of perceived STD risk (e.g., with sex partners known
to have STD or who have other partners), thereby complicating
valid comparisons with those not using condoms, who
often have lower sexual risks (133;134). Furthermore,
valid estimates of condom effectiveness can be obtained
only when users and nonusers have similar levels of
exposure to infected partners as illustrated in a recent
study of gonorrhea and chlamydia (123). This study
showed a protective effect for condoms among persons
whose sex partners were known to be infected, but not
among those whose partners were not known to be infected.
Data on whether partners have HPV infection has not
been available for most studies of condoms and HPV
infection.

Studying the relationship between condom
use and HPV infection is particularly difficult compared
to other STD. In contrast to viral STD such as HIV
and genital herpes for which highly accurate blood
tests allow conclusive determination of infection,
accurate blood tests for genital HPV infection do not
exist at present. The detectability of HPV DNA in a
given individual varies over time (68;135); therefore,
determining if a person is infected or if an infection
is new or pre-existing is very difficult. Finally,
it is also difficult to study outcomes that take many
years to develop (e.g., high-grade cervical cell abnormalities,
invasive cervical cancer). The optimal study design
to ensure valid measurements is a randomized, controlled
trial. However, because randomization (assigning some
individuals to use condoms and assigning others not
to use condoms) can be problematic and potentially
unethical (118), this study design is rarely used.

We evaluated 46 peer-reviewed publications
in English available after January 1966 that included
information on the association between condom use and
HPV infection or a sequelae (e.g., genital warts, HPV-associated
lesions including cervical cancer precursors, or invasive
cervical cancer) (21;26;28;30;31;39;46;48;49;52;84;86;87;136-168).
We excluded publications that evaluated HIV-infected
persons or used only HPV blood tests. These studies
represent a variety of geographic areas and populations.
Of the 46 studies, 23 evaluated condom use and prevalent
or incident HPV infection by detection of HPV DNA,
and 25 evaluated sequelae of infection. The studies
of sequelae included five that measured clinical findings
of warts or HPV-suggestive lesions on the external
genital skin, 10 that measured low- or combined low-grade
and high-grade cervical cell abnormalities, six that
evaluated high-grade cervical cell abnormalities, and
nine that evaluated cervical cancer, six of which were
studies of invasive cervical cancer. In most studies,
condom use was generally defined broadly, as “ever
versus never” or “use versus non-use”;
in some studies the definition of condom use was not
specified. Only 14 studies measured consistent condom
use, and none measured correct use. Forty studies were
cross-sectional (so the temporal relationship between
condom use and HPV outcome could not be easily determined);
two studies were randomized.

Of the 23 studies that measured HPV infection,
18 were conducted in women only, four in men only,
and one in both women and men. Estimates of the level
of risk reduction varied broadly. Three studies in
women reported a protective effect of condoms which
was statistically significant (151;152;153). None of
the studies measured exposure to infected partners.

Of the 10 studies that measured either
low-grade cervical cell abnormalities, or combined
low-grade and high-grade cervical cell abnormalities,
one study found a statistically significant reduction
in cervical cell abnormalities.

Of the five studies that measured external
genital HPV-associated lesions, three evaluated women
(all genital warts), three evaluated men (one with
genital warts and two with HPV suggestive lesions of
the penis), and one evaluated both women and men (48;139;142;145;164)
Of the three studies in women, one found a statistically
significant reduction (30%) in genital warts (164)
and one found a reduction in risk that was not statistically
significant (142). All three studies in men found statistically
significant protection with levels ranging from 30–70%
(48;145;164).

Of the six studies that measured cervical
cancer precursors (including carcinoma in situ), two
studies found a reduction of risk which was statistically
significant (136;137;146;154;158;166). Nine studies
evaluated women with cervical cancer, six of which
were invasive cervical cancer (138;140;143;149;155;156;159;162;166).
Of the nine studies, seven found a reduction in risk
of cancer in women using condoms, two of which were
statistically significant. The reduction in risk ranged
from 20–80%.

Three studies evaluated the effect
of condoms on clearance of HPV DNA or HPV-associated
lesions; all of these studies found a benefit of
condom use for both men and women (145;167;168). Two
of these
studies were the first studies of condoms and HPV
infection to be conducted as randomized controlled
trials, an
approach which can substantially reduce bias. In
the randomized studies, monogamous couples were randomized
to condom use or nonuse; females with a male partner
that used condoms had significantly higher rates
of
clearance of both HPV infection (53% vs. 35%), and
cervical cell changes (23% vs. 4%) than the females
whose male partner did not use condoms (168). Also,
men in the study had significantly faster regression
of genital lesions consistent with HPV infection (167).

Available studies suggest that condoms
reduce the risk of the clinically important outcomes
of genital warts and cervical cancer. One possible
explanation for the protective effect of condoms against
warts and cancer is that condom use could reduce the
quantity of HPV transmitted or decrease the likelihood
of re-exposure, thereby decreasing the chance of developing
clinical disease (14;118;168). An alternative explanation
is that condom use may reduce exposure to a co-factor
for cervical cancer, such as chlamydia or genital herpes,
thereby reducing the chance of cervical cancer (81;82;119-122;124;169).

However, all published epidemiologic
studies have significant methodologic limitations which
make the effect of condoms in prevention of HPV infection
unknown. As noted on page 14, three studies on genital
HPV and condom use showed a protective effect, but
most studies on genital HPV infection and condom use
did not show a protective effect.

Given these observations, as well as
the facts that laboratory studies show that latex condoms
provide a barrier to HPV and that most genital HPV
in men is located on areas of the skin covered by a
condom, the cumulative body of available scientific
evidence suggests that condoms may provide some protection
in preventing transmission of HPV infections but that
protection is partial at best. The available scientific
evidence is not sufficient to recommend condoms as
a primary prevention strategy for the prevention of
genital HPV infection. There is evidence that indicates
that the use of condoms may reduce the risk of cervical
cancer.

Microbicides
Evaluation of the ability
of microbicides to prevent genital HPV infection has
been hampered by the difficulties with in vitro cultivation
of HPV (14). Recent laboratory work suggests that some
compounds may inhibit HPV (170-174). There are also
some reports of a potential effect of microbicides
in the prevention of cervical cancer (143;156;159;172;175).
Future microbicides may be effective in preventing
HPV, as well as other sexually transmitted infections.
Clinical studies of some of the compounds found to
have an effect on HPV in the laboratory are underway.

Reduction of Sexual Behavior Risk
Because
of the important role sexual contact plays in the transmission
of genital HPV infection and because of limited evidence
that other prevention approaches are highly effective,
the most effective personal prevention approach is
to avoid contact with genital HPV infection by limiting
the number and type of sexual partners. The studies
that demonstrate genital HPV transmission by sexual
intercourse and other genital contact support the premise
that abstaining from all genital contact, including
non-penetrative contact, is the most effective approach
to preventing infection (21;88;90;176). However, no
studies have evaluated the effectiveness of programs
which promote limiting the number of partners in preventing
genital HPV infection. For individuals who choose to
be sexually active, data from studies of both HPV incidence
and prevalence support the notion that long-term monogamy
with a single partner is likely to be the next most
effective approach to prevent infection.

The choice of partner is likely to be
important in the success of this approach because approximately
20% of women with only one lifetime sex partner have
HPV infection (25;177). Knowing if a man is infected
with HPV is difficult because most infected men are
asymptomatic (64). Furthermore, testing men to find
out if they are infected is impractical because of
uncertain sensitivity of HPV testing in men and the
lack of a test which has been approved for this purpose.
The most important factors that decrease the likelihood
that a man is infected with genital HPV include his
having had a limited number of prior sex partners (45;52),
possibly having a longer period of time since his last
partner (allowing prior infections to spontaneously
resolve) (21), and being circumcised (46;52). The most
important factor that may decrease the likelihood that
a woman is infected with genital HPV include her having
had a limited number of prior sex partners (21;28).
In addition, characteristics which may increase the
chance that a partner is infected with genital HPV
include the presence of genital warts, an abnormal
Pap test in women, and immune suppression (64). However,
determining a partner’s sexual history or assuring
their monogamy in a long-term relationship is sometimes
difficult, a problem that could reduce the effectiveness
of partner selection approaches to prevention.

Vaccines
In contrast to other prevention
approaches, vaccines can reduce susceptibility in uninfected
partners by stimulating the immune system. A variety
of HPV vaccines are under investigation which may provide
immunity to a combination of high-risk or high- and
low-risk HPV types (178). The goals of HPV vaccines are
to prevent HPV-associated sequelae including genital
warts, cervical cancer precursors, and cervical cancer
by preventing HPV infection altogether or by reducing
the chance of persistent infection if infection does
occur. A recently completed economic model concluded
that vaccination for HPV, in combination with continued
cervical cancer screening, would be a cost effective
health intervention (179). In addition, a recent
study projected that an effective vaccine could prevent
1,300 deaths annually from cervical cancer if all
12-year-old girls currently living in the United
States were vaccinated (180). Although an effective
HPV vaccine would be a major advance in approaches
to HPV prevention, it would not replace other prevention
strategies such as cervical cancer screening or protective
sexual behaviors since vaccines would not work for
all genital HPV types and would likely not be 100%
effective.

HPV vaccines have shown encouraging success
in clinical trials (181). Recently, a vaccine for HPV-16
given to adolescent girls demonstrated 91% efficacy
in preventing HPV-16 infection and essentially complete
protection (100% efficacy) in preventing persistent
HPV-16 infection. Although there were only a few cases,
the vaccine also appears promising in the prevention
of cervical cancer precursors (181). Studies of other
formulations of HPV-16 vaccines as well as vaccines
with multiple HPV types are underway and are likely
to provide an important new approach for genital HPV
prevention within the next several years. Surveys of
young women who are potential candidates for an HPV
vaccine indicate that they have positive attitudes
about receiving a vaccine (182).

Prevention of Cervical Cancer
Decades
ago, cervical cancer was one of the most common and
deadly cancers in women in the United States (97;183).
In the past 40 years, widespread cervical cancer screening
using the Pap test, and treatment of precancerous cervical
abnormalities have resulted in a dramatic decrease
in the incidence and mortality due to cervical cancer
in the United States (97;183). The purpose of screening
with the Pap test is to detect cervical abnormalities
that can be treated, thereby preventing progression
to invasive cervical cancer, and also to detect invasive
cervical cancer at a very early stage. Progression
from cervical cancer precursor lesions to invasive
cancer is a slow process, estimated to take 10–15
years (16). If detected early and managed promptly,
survival rates for cervical cancer are over 90%. In
2003, an estimated 12,200 women in the U.S. will develop
cervical cancer and an estimated 4100 women will die
from the disease (66). Approximately half of the cases
will occur in women who have never been screened, and
an additional 10% will occur in women not screened
within the past 5 years (2). A recent national survey
indicated that cervical cancer screening is not adequate
among some women in the U.S; approximately 18% of women
have not had a Pap test in the last 3 years (184).
The most important factors associated with inadequate
cervical cancer screening include absence of a usual
source of health care, lack of health insurance, and
immigration to the U.S. in the last 10 years. Other
factors included older age, low income, low level of
education, presence of chronic disabilities, and Asian
and American Indian/Alaska Native race/ethnicity (184).
Death rates from cervical cancer in the U.S. are higher
among foreign-born women than women born in the U.S.
(185).

New technologies including liquid-based
cytology and testing for high-risk HPV types may offer
potential advantages over conventional Pap testing.
The American Cancer Society and other organizations have
incorporated these technologies into new guidelines
for cervical cancer screening (115;186;187). However,
the largest gain in reducing the burden of cervical
cancer incidence and deaths could best be achieved
by increasing screening rates among women who have
never or rarely been screened (186).

Other Resources:

Note: Online Dating Magazine does not sell text links anywhere on the site, so please don't email asking about text links. Any links we have are affiliate links, resources we find useful, links to other sites we run or long-time magazine sponsors. We do have graphic ad options in our Advertising section.